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The intracluster light analysis of the most evolved systems of galaxies: fossil groups

Nícolas O. L. de Oliveira, Yolanda Jiménez-Teja, Renato A. Dupke, Eleazar R. Carrasco, Anton M. Koekemoer, Yuanyuan Su, Jose Manuel Vilchez, Jimmy A. Irwin, Eric D. Miller, Lucas E. Johnson

TL;DR

The study investigates whether fossil groups at $z\sim0.1$ are truly ancient and undisturbed by applying CHEFs/CICLE-based intracluster light (ICL) mapping to three FG candidates using HST/ACS imaging in F435W and F606W and GMOS spectroscopy. ICL fractions are measured across wavelengths, revealing an increasing trend with wavelength for two systems, consistent with old, relaxed FG evolution, while RXJ1136 shows no such trend and is not a bona fide FG. The results support ICL as an independent diagnostic of dynamical state and FG purity beyond the traditional magnitude-gap criterion, with implications for understanding galaxy-group assembly and the fossil phase. Together, the findings suggest that ICL-based analyses can refine FG classifications and trace their merger histories in the local universe.

Abstract

We present the analysis of the intracluster light (ICL) in three fossil groups (FG), RXJ085640.72+055347.36, RX J1136+0713, and RX J1410+4145, at z ~ 0.1. We used two optical broad-band filters, F435W and F606W, observed with the Hubble Space Telescope and spectroscopic data obtained with the Gemini Multi-Object Spectrograph to generate the ICL maps and measure the ICL fraction using CICLE, an algorithm developed to disentangle the ICL from the light of galaxies. We found ICL fractions of 9.9% - 14.4%, 3.8% - 6.1%, and 4.7% - 10.7% for RXJ0856, RXJ1136, and RXJ1410, respectively. This behavior is not consistent with the presence of the ICL fraction excess previously observed in merging clusters and also inconsistent with the constant ICL fraction distribution characteristic of relaxed systems, although the values found are within the typical range expected for the latter. Instead, they show a significantly increasing trend with wavelengths over ~ 3800 - 5500A, indicating that fossil groups are indeed old and undisturbed systems, even compared with regular relaxed clusters.

The intracluster light analysis of the most evolved systems of galaxies: fossil groups

TL;DR

The study investigates whether fossil groups at are truly ancient and undisturbed by applying CHEFs/CICLE-based intracluster light (ICL) mapping to three FG candidates using HST/ACS imaging in F435W and F606W and GMOS spectroscopy. ICL fractions are measured across wavelengths, revealing an increasing trend with wavelength for two systems, consistent with old, relaxed FG evolution, while RXJ1136 shows no such trend and is not a bona fide FG. The results support ICL as an independent diagnostic of dynamical state and FG purity beyond the traditional magnitude-gap criterion, with implications for understanding galaxy-group assembly and the fossil phase. Together, the findings suggest that ICL-based analyses can refine FG classifications and trace their merger histories in the local universe.

Abstract

We present the analysis of the intracluster light (ICL) in three fossil groups (FG), RXJ085640.72+055347.36, RX J1136+0713, and RX J1410+4145, at z ~ 0.1. We used two optical broad-band filters, F435W and F606W, observed with the Hubble Space Telescope and spectroscopic data obtained with the Gemini Multi-Object Spectrograph to generate the ICL maps and measure the ICL fraction using CICLE, an algorithm developed to disentangle the ICL from the light of galaxies. We found ICL fractions of 9.9% - 14.4%, 3.8% - 6.1%, and 4.7% - 10.7% for RXJ0856, RXJ1136, and RXJ1410, respectively. This behavior is not consistent with the presence of the ICL fraction excess previously observed in merging clusters and also inconsistent with the constant ICL fraction distribution characteristic of relaxed systems, although the values found are within the typical range expected for the latter. Instead, they show a significantly increasing trend with wavelengths over ~ 3800 - 5500A, indicating that fossil groups are indeed old and undisturbed systems, even compared with regular relaxed clusters.

Paper Structure

This paper contains 7 sections, 2 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Data
  3. HST imaging
  4. Gemini spectra
  5. Analysis
  6. Discussion
  7. Conclusions

Figures (2)

  • Figure 1: Original images of RXJ0856 (left), RXJ1136 (center), and RXJ1410 (right) in the F606W filter and their corresponding galaxy members in green circles. Saturated stars are masked in white circles. North is up, east is left.
  • Figure 2: ICL fractions measured for the three FGs added to a sample of galaxy clusters and groups analyzed by jimenez-teja2018jimenez-teja2021 and deoliveira2022 at rest-frame wavelength. Merging systems are represented in red and relaxed systems are represented in blue. FGs systems are represented in black symbols with corresponding error bars. We also include the bona fide FG (RXJ1007, black triangle) analyzed by dupke2022.